Silicon photonics is using silicon integrated circuits technology so that data can be sent and received through light guided in a waveguide. Such devices, fabricated on a silicon-on-insulator (SOI) wafer and operating at the 1.3 μm and 1.55 μm telecom wavelength, offer the potential for on-chip monolithic integration of telecommunication systems. In particular, developing photodetectors for the telecom wavelength using standard Silicon-on-Insulator Complementary Metal-Oxide-Semiconductor (SOI CMOS) manufacturing processes plays an essential role towards the potential.
Among requirements for the photodetectors to be integrated in the telecommunication system, silicon photodetectors are required to operate at frequency range beyond 20 GHz, which has already been demonstrated up to 50 GHz. Another target requirement for the photodetectors is low-voltage operation, i.e., bias voltage <5V and as low as 1V for advanced CMOS generation. This has also been demonstrated, as Ge doped photodetectors can operate with bias voltage in 1-15V at telecom wavelength. A further requirement is a sensitivity of the photodetectors that allows detection of a low current on the order of 1 μA. Therefore, the dark current (i.e. noise, a small current produced when no light is present) must be minimized with respect to photocurrent signals (i.e., current generated when light is absorbed in the photodiode) to maximize the signal-to-noise ratio.